The present invention provides an improved and low cost tapered waveguide suitable for use in integrated optics applications. More specifically, an optical waveguide having a tapered structure and a process for manufacturing the same from a relatively low cost substrate material is highly desirable in the electro-optical field.
With the increased application of integrated optics, there has been created a demand to improve the manufacturing processes of optical waveguides. The advantages of optical waveguides and their integration in electro-optical devices is well known, and has become even more significant in the miniaturization of various electro-optical devices. Such systems are described, e.g., by S. E. Miller in "Integrated Optics: An Introduction", Bell System Technical Journal, Vol. 48 (1969), pp. 2059-2069, and the manner in which they can be manufactured has been described by E. G. Spencer et al., "Ion Beam Techniques for Device Fabrication", Journal of Vacuum Science and Technology, Vol. 8 (1972), pp. 552-570. Recently, semiconductor lasers have been significantly reduced in size and improved, and now provide a source of coherent electromagnetic radiation which requires waveguides for transmitting such radiation, for example, as a communication medium. Proposed optical communication systems may comprise light sources, waveguides and active components such as, e.g., modulators, deflectors and switches. Waveguides may be of a type known as optical fibers, or, more recently, they have taken the form of patterned transparent films on a substrate, the latter type being particularly suited for miniaturized, complex optical circuits. The ability for the waveguides to carry a large amount of information across a wide band of frequencies suggests numerous advantages over the more conventional electrical waveguide structures. As can be readily appreciated, it is highly desirable that the tapered waveguide provide an efficient, low cost coupling with low loss of energy.
The prior art has recognized the necessity and advantages of utilizing tapered waveguide structures for coupling with light sources and for interfacing or coupling two optical waveguides having a different cross-sectional area. However, considerable problems have existed for providing this coupling arrangement, and the prior art has resorted to not only tapering a waveguide in a substrate such as lithium niobate, but also has attempted to produce conical gradient lenses such as disclosed in U.S. Pat. No. 4,278,322.
U.S. Pat. No. 4,372,641 discloses a conventional method of making a tapered waveguide structure wherein a mask is deposited on a substrate, leaving exposed the desired optical path whose width diminishes. Side walls of the mask may be straight or undercut, and waveguide material such as, for example, an appropriate glass, can be deposited through the mask, e.g., by electron beam deposition.
The disclosure of U.S. Pat. No. 4,262,995, which represents the work of one of the co-inventors, Gregory L. Tangonan, is of interest for its discussion of the formation of optical waveguide sections and tapered or horn-shaped wave transition sections in a soda-lime glass substrate by an ion exchange process where, for example, a metal ion is substituted for the sodium ion in the glass substrate to form the waveguide. Thus, the prior art has recognized the advantages of tapered optical waveguides and their formation in relatively inexpensive substrate material such as soda-lime glass, but has still not been able to optimize the process of producing the tapered waveguide, nor the necessity for fabricating planar waveguides that usually require tedious handling and polishing of the guide surfaces at an angle to form the tapered guide. Finally, reference is made to U.S. Pat. No. 4,169,009, of general interest, to disclose waveguide formations through the use of ion beam milling and precise mechanical and chemomechanical manufacturing methods.
There is still a need in the prior art to provide an improved process of making and producing a tapered waveguide.